1. Field of the Invention
The present invention relates generally to printmaking engraving and more specifically to software for creating printmaking engraving.
2. The Prior Art
Engraving is the practice of incising a design onto a hard, flat surface, by cutting grooves into it. The result may be a decorative object in itself, as when silver or gold are engraved, or in art may provide an intaglio printing plate in printmaking of copper or another metal.
Traditional engravers use a hardened steel tool called a burin to cut the design into the surface, most traditionally a copper plate. Gravers come in a variety of shapes and sizes that yield different line types. The burin produces a unique and recognizable quality of line that is characterized by its steady, deliberate appearance and clean edges. The angle tint tool has a slightly curved tip that is commonly used in printmaking. Florentine liners are flat-bottomed tools with multiple lines incised into them, used to do fill work on larger areas. Flat gravers are used for doing fill work on letters, as well as most musical instrument engraving work. Round gravers are commonly used on silver to create bright cuts (also called bright-cut engraving), as well as other hard-to-cut metals such as nickel and steel. Burins are either square or elongated diamond-shaped and used for cutting straight lines. Other tools such as mezzotint rockers, roulets and burnishers are used for texturing effects.
Traditionally, engravers created darker areas by making an area of many very thin parallel lines (called hatching). When two sets of parallel line hatchings intersected each other for higher density, the resultant pattern was known as cross-hatching. The modern discipline of hand engraving survives largely in a few specialized fields. In most of industrial uses like production of Intaglio plates for commercial applications hand engraving was replaced with milling using CNC engraving/milling machines.
Another application of modern engraving is found in the printing industry. There, every day thousands of pages are engraved in rotogravure cylinders, typically a steel base with a copper layer of about 0.1 mm in which the image is transferred. After engraving, the image is protected with an approximately 6 μm chrome layer. Using this process the image will survive million plus copies in high speed printing presses.
Typically the image is created in some PDF-like format and enters a workflow where it is processed and automatically imposed to the huge printing cylinders. Today up to 192 pages can be engraved on the same cylinder. Since the cylinder serves to print one color, four cylinders are typically used to print one side of the substrate. Rotogravure has a major share in publication, packaging and decorative printing. Gravure cylinders are typically engraved digitally by a diamond tipped or laser etching machine.
Engraving machines such as the K500 (packaging) or K6 (publication) by Hell Gravure Systems use a diamond stylus to cut cells. Each cell creates one printing dot later in the process. A K6 can have up to 18 engraving heads each cutting 8.000 cells per second to an accuracy of 0.1 μm and below. They are of course fully computer controlled and the whole process of cylinder making is fully automated. Laser engraving machines are also in use.
Laser engraving is the practice of using lasers to engrave or mark an object (it is also sometimes incorrectly described as etching, which involves the use of acid or a similar chemical). The technique can be very technical and complex, and often a computer system is used to drive the movements of the laser head. Despite this complexity, very precise and clean engravings can be achieved at a high rate. The technique does not involve tool bits which contact the engraving surface and wear out. This is considered an advantage over alternative engraving technologies where bit heads have to be replaced regularly.
The impact of laser engraving has been more pronounced for specially-designed “laserable” materials. These include polymer and novel metal alloys.
A laser engraving machine can be thought of as three main parts: a laser, a controller, and a surface. The laser is like a pencil—the beam emitted from it allows the controller to trace patterns onto the surface. The controller (usually a computer) controls the direction, intensity, speed of movement, and spread of the laser beam aimed at the surface. The surface is picked to match what the laser can act on.
There are three main genres of engraving machines: The most common is the X-Y table where, usually, the work piece (surface) is stationary and the laser moves around in X and Y directions drawing vectors. Sometimes the laser is stationary and the work piece moves. Sometimes the work piece moves in the Y axis and the laser in the X axis. A second genre is for cylindrical work pieces (or flat work pieces mounted around a cylinder) where the laser effectively traverses a fine helix and on/off laser pulsing produces the desired image on a raster basis. In the third method, both the laser and work piece are stationary and galvo mirrors move the laser beam over the work piece surface. Laser engravers using this technology can work in either raster or vector mode.
The point where the laser (the terms “laser” and “laser beam” may be used interchangeably) touches the surface should be on the focal plane of the laser's optical system, and is usually synonymous with its focal point. This point is typically small, perhaps less than a fraction of a millimeter (depending on the optical wavelength). Only the area inside this focal point is significantly affected when the laser beam passes over the surface. The energy delivered by the laser changes the surface of the material under the focal point. It may heat up the surface and subsequently vaporize the material, or perhaps the material may fracture (known as “glass” or “glass up”) and flake off the surface. This is how material is removed from the surface to create an engraving.